Ajax Select Boxes

I have selection fields in a content type.
I want that when i select any option from 1st field , its related options should fill in 2nd field through ajax.
My first questions is , can i do it with cck module?
If yes then please tell me the way.
If no then please tell me that which module can do it.

I can do it by custom programming, but i will like to use drupal module. This may safe my time :)